Vacuum liners for defining a plasma path have been constructed using thin wall bellows sections made of stainless steel. These bellows sections offer high strength while forming a closed loop having sufficiently high electrical resistance that penetration times are acceptably low for magnetic fields generated by poloidal, toroidal or other associated magnetic systems for containing and energizing the plasma. Unfortunately, the thin bellows sections, when used in a high energy plasma environment may experience local surface melting due to plasma contact. The melting results in structural weakness and vacuum leaks in the liner.
In one attempt to prevent melting of the bellows sections, short pieces of stainless steel rod limiters were installed on the inside surface of the sections. By absorbing the plasma energy, the rods protect the bellows. However, contact with the plasma causes erosion of the metal rods, resulting in contamination of the plasma due to the introduction of metal impurities which radiate and cause loss of power in the plasma. For further information regarding the structure and operation of such limiters, reference may be made to "Experimental and Computational Studies of Reversed-Field Pinch on TPE-IR(M)", by Ogawa et al. in "Proceedings of the 9th International Conference on Plasma Physics and Controlled Nuclear Fusion Research", Baltimore, 1982 (IAEA, Vienna, 1983), Vol. I, p. 575. Metallic limiters are also shown in U.S. Pat. No. 4,073,680.
In order to avoid the introduction of metal impurities into the plasma, carbon tiles have been used instead of the metal rods. However, the discrete tiles are not readily reliably fastened to the interior of the bellows. In another attempt to protect the bellows and avoid contamination of the plasma, rings of carbon tiles were placed at spaced locations in the vacuum chamber in the effort to make the plasma only contact the tiles. However, the expected reduction of the heat level on the bellows was not found, and arcing occurred between the liner and the tiles which resulted in damage to the liner. For further information regarding such limiters, reference may be-made to "Mushroom Limiter Studies in ZT-40M", Downing et al., Bull. Am. Phy. Soc., 27, 1108 (1982); and "Temperature and Resistivity of the ZT-40M RFP with Poloidal Limiters", Haberstich et al., Bull. Am. Phy., 28, 1097.